My take from this is that, in a long run, if unaided group would keep using their brains for tasks, they would develop their brain because of training, while AI group would eventually lose even their existing skills (at least when it comes to writing essays). Because if you don't use your brains, those connections on the brains wouldn't be needed either.
Are we to assume that we are going to lose our skills
with these AIs? All I know is that once we acquire our skills, we have them for life, even after years of not using them, we always have them, because it's embedded in our subconscious mind.
A driver, even if he hasn't driven for years he can still drive; you never unlearn your skill, it just modifies. I don't know, but a writer is always a writer with or without the aid of AI, Whether it's your passion or a hobby, you have a writer's knack and spontaneity, you have it subconsciously.
There are ways to use AI that benefits people, but using that for your creative work, or anything that needs brains is just killing your brains.
Only drugs kill your brain, not a tool to enhance your creativity, that's all I know. I guess it depends on how you use these AIs.